Hitherto, there is an image forming apparatus such as a multi-function peripheral (hereinafter referred to as “MFP”) or a printer. The image forming apparatus includes a fixing device. The fixing device heats a conductive layer of a fixing belt by an electromagnetic induction heating system (hereinafter referred to as “IH system”). The fixing device fixes a toner image to a recording medium by heat of the fixing belt. The conductive layer of the fixing belt generates heat by an induction current. In the fixing device, the heat capacity of the fixing belt is reduced in order to shorten a warming-up time and the like. The fixing device includes an auxiliary heat generation part in order to compensate insufficiency of the heat generation amount of the fixing belt. The auxiliary heat generation part concentrates magnetic flux at electromagnetic induction heating and increases the heat generation amount of the fixing belt. The auxiliary heat generation part is formed of a magnetic material. For example, the magnetic material is a magnetic shunt alloy. The magnetic characteristic of the magnetic shunt alloy changes according to temperature. The magnetic shunt alloy changes from ferromagnetic to paramagnetic at the Curie point. The magnetic shunt alloy generates heat by itself. There is a possibility that the magnetic shunt alloy loses magnetic properties, and the heating efficiency of the fixing belt is reduced.